Parse Dart placeholders based on their context

sqlparser/lib/src/ast/ast.dart

@@ -193,7 +193,7 @@ abstract class AstVisitor<T> {
   T visitMoorFile(MoorFile e);
   T visitMoorImportStatement(ImportStatement e);
   T visitMoorDeclaredStatement(DeclaredStatement e);
-  T visitInlineDartCode(InlineDart e);
+  T visitDartPlaceholder(DartPlaceholder e);
 }
 
 /// Visitor that walks down the entire tree, visiting all children in order.
@@ -316,7 +316,7 @@ class RecursiveVisitor<T> extends AstVisitor<T> {
   T visitMoorDeclaredStatement(DeclaredStatement e) => visitChildren(e);
 
   @override
-  T visitInlineDartCode(InlineDart e) => visitChildren(e);
+  T visitDartPlaceholder(DartPlaceholder e) => visitChildren(e);
 
   @protected
   T visitChildren(AstNode e) {

sqlparser/lib/src/ast/clauses/limit.dart

@@ -1,5 +1,8 @@
 part of '../ast.dart';
 
+/// Base for limit statements. Without moor extensions, only [Limit] will be
+/// parsed. With moor extensions, a [DartLimitPlaceholder] can be emitted as
+/// well.
 abstract class LimitBase implements AstNode {}
 
 class Limit extends AstNode implements LimitBase {

sqlparser/lib/src/ast/clauses/ordering.dart

@@ -1,7 +1,16 @@
 part of '../ast.dart';
 
-class OrderBy extends AstNode {
-  final List<OrderingTerm> terms;
+/// Base for `ORDER BY` clauses. Without moor extensions, ony [OrderBy] will be
+/// parsed. Otherwise, [DartOrderByPlaceholder] can be parsed as well.
+abstract class OrderByBase extends AstNode {}
+
+/// Base for a single ordering term that is a part of a [OrderBy]. Without moor
+/// extensions, only [OrderingTerm] will be parsed. With moor extensions, a
+/// [DartOrderingTermPlaceholder] can be parsed as well.
+abstract class OrderingTermBase extends AstNode {}
+
+class OrderBy extends AstNode implements OrderByBase {
+  final List<OrderingTermBase> terms;
 
   OrderBy({this.terms});
 
@@ -19,7 +28,7 @@ class OrderBy extends AstNode {
 
 enum OrderingMode { ascending, descending }
 
-class OrderingTerm extends AstNode {
+class OrderingTerm extends AstNode implements OrderingTermBase {
   final Expression expression;
   final OrderingMode orderingMode;
 

sqlparser/lib/src/ast/expressions/aggregate.dart

@@ -74,7 +74,7 @@ class NamedWindowDeclaration with Referencable {
 class WindowDefinition extends AstNode {
   final String baseWindowName;
   final List<Expression> partitionBy;
-  final OrderBy orderBy;
+  final OrderByBase orderBy;
   final FrameSpec frameSpec;
 
   WindowDefinition(

sqlparser/lib/src/ast/moor/inline_dart.dart

@@ -8,40 +8,45 @@ part of '../ast.dart';
 ///  1. expressions: Any expression can be used for moor: `SELECT * FROM table
 ///  = $expr`. Generated code will write this as an `Expression` class from
 ///  moor.
-///  2. limits
-///  3. A single order-by clause
-///  4. A list of order-by clauses
-abstract class InlineDart extends AstNode {
+///  2. limits, which will be exposed as a `Limit` component from moor
+///  3. A single order-by clause, which will be exposed as a `OrderingTerm` from
+///  moor.
+///  4. A list of order-by clauses, which will be exposed as a `OrderBy` from
+///  moor.
+abstract class DartPlaceholder extends AstNode {
   final String name;
 
   DollarSignVariableToken token;
 
-  InlineDart._(this.name);
+  DartPlaceholder._(this.name);
 
   @override
   final Iterable<AstNode> childNodes = const Iterable.empty();
 
   @override
-  T accept<T>(AstVisitor<T> visitor) => visitor.visitInlineDartCode(this);
+  T accept<T>(AstVisitor<T> visitor) => visitor.visitDartPlaceholder(this);
 
-  bool _dartEquals(covariant InlineDart other);
+  bool _dartEquals(covariant DartPlaceholder other) => true;
 
   @override
-  bool contentEquals(InlineDart other) {
+  bool contentEquals(DartPlaceholder other) {
     return other.name == name && other._dartEquals(other);
   }
 }
 
-class InlineDartExpression extends InlineDart implements Expression {
-  InlineDartExpression({@required String name}) : super._(name);
-
-  @override
-  bool _dartEquals(InlineDartExpression other) => true;
+class DartExpressionPlaceholder extends DartPlaceholder implements Expression {
+  DartExpressionPlaceholder({@required String name}) : super._(name);
 }
 
-class InlineDartLimit extends InlineDart implements LimitBase {
-  InlineDartLimit({@required String name}) : super._(name);
-
-  @override
-  bool _dartEquals(InlineDartLimit other) => true;
+class DartLimitPlaceholder extends DartPlaceholder implements LimitBase {
+  DartLimitPlaceholder({@required String name}) : super._(name);
+}
+
+class DartOrderingTermPlaceholder extends DartPlaceholder
+    implements OrderingTermBase {
+  DartOrderingTermPlaceholder({@required String name}) : super._(name);
+}
+
+class DartOrderByPlaceholder extends DartPlaceholder implements OrderByBase {
+  DartOrderByPlaceholder({@required String name}) : super._(name);
 }

sqlparser/lib/src/ast/statements/select.dart

@@ -9,7 +9,7 @@ class SelectStatement extends Statement with CrudStatement, ResultSet {
   final GroupBy groupBy;
   final List<NamedWindowDeclaration> windowDeclarations;
 
-  final OrderBy orderBy;
+  final OrderByBase orderBy;
   final LimitBase limit;
 
   /// The resolved list of columns returned by this select statements. Not

sqlparser/lib/src/reader/parser/crud.dart

@@ -272,22 +272,41 @@ mixin CrudParser on ParserBase {
     return declarations;
   }
 
-  OrderBy _orderBy() {
+  OrderByBase _orderBy() {
     if (_matchOne(TokenType.order)) {
       _consume(TokenType.by, 'Expected "BY" after "ORDER" token');
-      final terms = <OrderingTerm>[];
+      final terms = <OrderingTermBase>[];
       do {
         terms.add(_orderingTerm());
       } while (_matchOne(TokenType.comma));
+
+      // If we only hit a single ordering term and that term is a Dart
+      // placeholder, we can upgrade that term to a full order by placeholder.
+      // This gives users more control at runtime (they can specify multiple
+      // terms).
+      if (terms.length == 1 && terms.single is DartOrderingTermPlaceholder) {
+        final termPlaceholder = terms.single as DartOrderingTermPlaceholder;
+        return DartOrderByPlaceholder(name: termPlaceholder.name);
+      }
+
       return OrderBy(terms: terms);
     }
     return null;
   }
 
-  OrderingTerm _orderingTerm() {
+  OrderingTermBase _orderingTerm() {
     final expr = expression();
+    final mode = _orderingModeOrNull();
 
-    return OrderingTerm(expression: expr, orderingMode: _orderingModeOrNull());
+    // if there is no ASC or DESC after a Dart placeholder, we can upgrade the
+    // expression to an ordering term placeholder and let users define the mode
+    // at runtime.
+    if (mode == null && expr is DartExpressionPlaceholder) {
+      return DartOrderingTermPlaceholder(name: expr.name)
+        ..setSpan(expr.first, expr.last);
+    }
+
+    return OrderingTerm(expression: expr, orderingMode: mode);
   }
 
   @override
@@ -326,8 +345,8 @@ mixin CrudParser on ParserBase {
       // no offset or comma was parsed (so just LIMIT $expr). In that case, we
       // want to provide additional flexibility to the user by interpreting the
       // expression as a whole limit clause.
-      if (first is InlineDartExpression) {
-        return InlineDartLimit(name: first.name)
+      if (first is DartExpressionPlaceholder) {
+        return DartLimitPlaceholder(name: first.name)
           ..setSpan(limitToken, _previous);
       }
       return Limit(count: first)..setSpan(limitToken, _previous);
@@ -457,7 +476,7 @@ mixin CrudParser on ParserBase {
     final leftParen = _previous;
 
     String baseWindowName;
-    OrderBy orderBy;
+    OrderByBase orderBy;
 
     final partitionBy = <Expression>[];
     if (_matchOne(TokenType.identifier)) {

sqlparser/lib/src/reader/parser/expressions.dart

@@ -322,7 +322,7 @@ mixin ExpressionParser on ParserBase {
       case TokenType.dollarSignVariable:
         if (enableMoorExtensions) {
           final typedToken = token as DollarSignVariableToken;
-          return InlineDartExpression(name: typedToken.name)
+          return DartExpressionPlaceholder(name: typedToken.name)
             ..token = typedToken
             ..setSpan(token, token);
         }

sqlparser/test/analysis/reference_resolver_test.dart

@@ -46,8 +46,9 @@ void main() {
     expect(context.errors, isEmpty);
 
     final select = context.root as SelectStatement;
-    final orderingTerm = select.orderBy.terms.single.expression as Reference;
-    final resolved = orderingTerm.resolved as ExpressionColumn;
+    final term = (select.orderBy as OrderBy).terms.single as OrderingTerm;
+    final expression = term.expression as Reference;
+    final resolved = expression.resolved as ExpressionColumn;
 
     enforceEqual(
       resolved.expression,

sqlparser/test/parser/inline_dart_test.dart

@@ -10,20 +10,20 @@ void main() {
       SelectStatement(
         columns: [StarResultColumn(null)],
         from: [TableReference('tbl', null)],
-        limit: InlineDartLimit(name: 'limit'),
+        limit: DartLimitPlaceholder(name: 'limit'),
       ),
       moorMode: true,
     );
   });
 
-  test('parses limit counts as expressions', () {
+  test('parses limit count as expressions', () {
     testStatement(
       r'SELECT * FROM tbl LIMIT $amount OFFSET 3',
       SelectStatement(
         columns: [StarResultColumn(null)],
         from: [TableReference('tbl', null)],
         limit: Limit(
-          count: InlineDartExpression(name: 'amount'),
+          count: DartExpressionPlaceholder(name: 'amount'),
           offsetSeparator: token(TokenType.offset),
           offset: NumericLiteral(3, token(TokenType.numberLiteral)),
         ),
@@ -31,4 +31,36 @@ void main() {
       moorMode: true,
     );
   });
+
+  test('parses ordering terms and ordering expressions', () {
+    testStatement(
+      r'SELECT * FROM tbl ORDER BY $term, $expr DESC',
+      SelectStatement(
+        columns: [StarResultColumn(null)],
+        from: [TableReference('tbl', null)],
+        orderBy: OrderBy(
+          terms: [
+            DartOrderingTermPlaceholder(name: 'term'),
+            OrderingTerm(
+              expression: DartExpressionPlaceholder(name: 'expr'),
+              orderingMode: OrderingMode.descending,
+            ),
+          ],
+        ),
+      ),
+      moorMode: true,
+    );
+  });
+
+  test('parses full order by placeholders', () {
+    testStatement(
+      r'SELECT * FROM tbl ORDER BY $order',
+      SelectStatement(
+        columns: [StarResultColumn(null)],
+        from: [TableReference('tbl', null)],
+        orderBy: DartOrderByPlaceholder(name: 'order'),
+      ),
+      moorMode: true,
+    );
+  });
 }